By John Kruzel and Andrew Chung

WASHINGTON (Reuters) -The U.S. Supreme Court on Tuesday grappled with a pair of cases from California and Michigan involving public officials blocking critics on social media, with the justices struggling to define when such conduct runs into constitutional limits on the government's ability to restrict speech.

Lower courts reached different conclusions in the two cases, reflecting the legal uncertainty over whether such social media activity is bound by the U.S. Constitution's First Amendment, which protects freedom of speech. Blocking users is a function often employed on social media to stifle critics.

The justices, hearing about three hours of arguments, focused on spelling out the circumstances for deciding whether public officials were acting in their personal capacity when blocking critics or engaged in a "state action." The First Amendment constrains government actors but not private individuals.

The first case involves two public school board trustees from Poway, California who appealed a lower court's ruling in favor of parents who sued them after being blocked from the personal accounts of the officials on X, called Twitter at the time, and Facebook (NASDAQ:META). The second case involves a Michigan man's appeal after a lower court rejected his lawsuit against a Port Huron city official who blocked him on Facebook.

Conservative Justice Samuel Alito cited a hypothetical town manager who puts a municipal seal on his own social media page and tells citizens to express their views. Alito told Hashim Mooppan, a lawyer for the school board officials, that his argument could let this town manager "block anybody who expresses criticism of what the town manager is doing, and thereby create the impression that everybody in town thinks the town manager is doing the right thing."

Mooppan urged the justices to embrace the "duty or authority" legal test that looks at whether officials operated their pages to fulfill official duties or used governmental authority to maintain them. Under this test, Mooppan argued, the social media activity of his clients was not governmental.

Liberal Justice Elena Kagan cited former President Donald Trump as an example, noting he did "a lot of government" on his Twitter account, sometimes even announcing policies.

"It was an important part of how he wielded his authority - and to cut a citizen off from that is to cut a citizen off from part of the way that government works," Kagan said.

The Supreme Court previously confronted the issue in 2021 in litigation over Trump's effort to block critics on Twitter. It declined to decide the matter, deeming the case moot after Trump left office.

President Joe Biden's administration sided with the officials in both cases argued on Tuesday. A ruling is expected by the end of June.

The California case involves Michelle O'Connor-Ratcliff and T.J. Zane, elected Poway Unified School District trustees. They blocked Christopher and Kimberly Garnier, parents of three local students, after they made hundreds of critical posts on issues including race and school finances. A judge sided with the couple. The San Francisco-based 9th U.S. Circuit Court of Appeals agreed.

In the Michigan case, Port Huron resident Kevin Lindke sued after City Manager James Freed blocked him from his public Facebook page following critical posts involving the COVID-19 pandemic. A judge ruled in favor of Freed. The Cincinnati-based 6th U.S. Circuit Court of Appeals agreed.

Some justices asked whether requiring public officials to include disclaimers on their personal pages making clear their social media activity is not governmental would help disentangle their private and public capacities.

Liberal Justice Ketanji Brown Jackson said she was struggling to understand "why the onus isn't on the government official to be clear about the capacity in which they're operating."

Conservative Justice Brett Kavanaugh told Victoria Ferres, an attorney for Freed, that considering everything an official posts about their job to be state action would be too broad, but wondered if a narrower category of postings such as announcing rules, directives or notices would suffice as official acts.

Ferres agreed: "If you have a duty to announce a rule and the only time that you ever do it is on the Facebook page, then there is going to be state action."

US Supreme Court weighs if public officials can block critics on social media 6